类水滑石Mg 3 Al 1- x Fe x 负载Ir催化剂在肉桂醛加氢反应中的应用:Fe的促进作用
摘要
Abstract Supported Ir catalysts were prepared using layered double hydrotalcite-like materials, such as Mg3Al1−xFex, containing Fe and Al species in varying amounts as supports. These Ir catalysts were applied for the selective hydrogenation of cinnamaldehyde (CAL). When x was changed from 0 (Ir/Mg3Al) to 1 (Ir/Mg3Fe), the rate of CAL hydrogenation reached a maximum at approximately x = 0.25, while the selectivity to unsaturated alcohol, i.e., cinnamyl alcohol, monotonously increased from 44.9% to 80.3%. Meanwhile, the size of the supported Ir particles did not change significantly with x, remaining at 1.7 ± 0.2 nm, as determined by transmission electron microscopy. The chemical state of Ir and Fe species in the Ir/Mg3Al1−xFex catalysts was examined by temperature programmed reduction by H2 and X-ray photoelectron spectroscopy. The surface of the supported Ir particles was also examined through the in-situ diffuse reflectance infrared Fourier-transform of a probe molecule of CO. On the basis of these characterization results, the effects of Fe doping to Mg3Al on the structural and catalytic properties of Ir particles in selective CAL hydrogenation were discussed. The significant factors are the electron transfer from Fe2+ in the Mg3Al1–xFex support to the dispersed Ir particles and the surface geometry.